GPS derived swathing guidance system

ABSTRACT

A swathing guidance system includes a controller storing data defining a desired vehicle path, a position detector subsystem such as a differential GPS receiver, and a display to graphically display current spatial parameters and corrective steering actions to place the vehicle on the desired path or to maintain it on the path. The controller periodically selects a future intercept point on the path and calculates a steering correction angle to point the vehicle toward the intercept point. The display includes a steering guide which displays the steering correction angle relative to the current heading and the current track error or distance from the desired path. The steering correction angle can alternatively be applied to an automatic steering mechanism to automatically maintain the vehicle on the desired path. In agricultural applications, the system is applicable to both parallel and contour cultivation modes.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to the area of agricultural soilworking and product application and, more particularly, to a guidancesystem and display to enable optimally driving swaths in rectangularfields, where parallel swathing is most efficient, and odd shapedfields, where contour swathing is more desirably employed.

[0002] As agricultural tractors have increased in size and horsepower,agricultural implements for cultivating soil and for applying treatmentproducts, such as fertilizers, herbicides, insecticides, or the like, tosoil and crops have also progressed from those which worked a singlecrop row to those which may work tens of rows simultaneously. Thereasons for such growth in agricultural equipment include efforts toincrease productivity through increases in fuel efficiency and decreasesin time required to work a given field. Thus, it is advantageous tocombine numerous agricultural operations per pass and to maximize theswath or soil working path width per pass. Another factor which affectsproductivity is crop yield per unit of field area. For this reason, itis desirable to maximize the percentage of arable land which iscultivated by avoiding gaps. At the same time, it is desirable to avoidoverlapping cultivation which wastes resources.

[0003] The cultivation of long straight, or parallel, crop rows isgenerally preferred since long rows minimize the number of turnaroundsat the ends of rows, and parallel rows are relatively easy to driveaccurately by the tractor operator. Flat fields with straight boundariesare especially suited to parallel crop rows. Fields with a more “hilly”character benefit from contour plowing in which the crop rows extendgenerally perpendicular to the gradient of the ground surface. Contourrows maximize moisture retention and minimize soil erosion. Also,contour rows are sometimes preferred for fields with irregularboundaries.

[0004] Parallel rows are easier to cultivate than contoured rows, andcrop rows are more accurately worked with a narrow implement frame thana wide frame. In order to increase accuracy in cultivation, variouspractices have involved to avoid gaps in cultivation and overlappingcultivation. Earliest practices included marking the edge of a “swath”in which an inert marking material is deposited during one pass from oneextremity of the tool frame. On the next pass, the operator wouldattempt to align an outer extremity of the frame with the previouslymarked line. Although generally successful, marking methods involve anadditional expense for the marking material and additionally the need tomonitor the amount of marking material on-board and replenish whenexhausted.

[0005] More recently, cultivation or swathing guidance has incorporatedposition data derived from satellite based global positioning systems.With current enhancements to the original GPS system, spatialresolutions of less than a meter are now possible. In general, GPStechniques have been applied to swath guidance in such a manner as tostore data defining a desired path, detect current position andsometimes heading, calculate a position offset or heading error, anddisplay a complement or opposite of the error to thereby guide theoperator in maintaining the desired path or returning to the desiredpath. In practice, it has been found that such an approach tends tocause the operator to overshoot the correction, resulting in oscillationabout the desired path. Such overshooting and oscillation is also foundin application of an error signal in such a manner to an automaticsteering mechanism. What is needed is a position detecting guidanceapproach which tends to lead the vehicle back onto the correct pathwithout overshoot. Such a guidance method should also be applicable toboth parallel cultivation as well as contour cultivation.

SUMMARY OF THE INVENTION

[0006] The present invention provides an improved system for vehicleguidance which is particularly well adapted for use in swathingguidance. The present invention includes a position detecting subsystemwhich provides data defining a currently detected position and aguidance controller which stores the positions detected by the positiondetecting system and is programmed with routines for generating andstoring data defining a reference path and a current path, forcalculating current speed and heading and an error in the currentposition, and for calculating a correction in heading to mostexpeditiously return the vehicle to the correct current path.

[0007] More specifically, the present invention repeatedly selects afuture intercept point on the desired path and calculates a headingcorrection to cause the vehicle to move toward the intercept point. Thecycle of selecting a new intercept point and heading correction isupdated often enough to cause the vehicle, if off-track, to “flare” intothe desired path. If the vehicle is already on the desired path or on aheading directly toward the intercept point, the method causes thevehicle to remain on the current heading.

[0008] In one embodiment of the invention, the apparatus includes adisplay including an arcuate array of steering indicators forming asteering guide along with a linear array of current position indicatorsto show relative distance and sense, or relative direction, from thedesired path. In another embodiment of the present invention, a steeringcorrection signal is applied to an automatic steering mechanism on thevehicle to automatically correct or maintain the vehicle on the desiredpath.

[0009] Another embodiment of the invention uses two straight LED arraysfor the steering error and cross track displays and seven-segment oralphanumeric displays for the menu and remote user entry throughswitches or a keypad.

[0010] The present invention makes use of automatic position detectiontechnologies, preferably including a satellite based global positioningsystem, such as the United States developed Navstar system, andenhancements thereof. Current versions of differential GPS systems areknown to have accuracies within less than one meter. Additionally, othertypes of position reckoning systems are known, such as those employingvarious kinds of odometers and rotation encoders, laser devices, and thelike, as well as conventional swath marking systems. The presentinvention contemplates incorporation of such other positioningdetermining systems within the novel methods described herein.

OBJECTS AND ADVANTAGES OF THE INVENTION

[0011] The principal objects of the present invention are: to provide animproved system for vehicle guidance; to provide such a system whichemploys position detecting technique, such as by reception of signalsfrom a satellite based global positioning system; to provide such asystem which is particularly well adapted for ground working vehicle,such as agricultural vehicles for soil working, fertilizing, spraying,irrigating, harvesting, and the like; to provide such a system whichminimizes gaps and overlaps in crop cultivation; to provide such asystem which calculates data defining desired paths of the vehicle,monitors the current position of the vehicle in relation to a desiredpath, and generates a steering correction signal to maintain the vehicleon the path or to return the vehicle to the path; to provide such asystem into which the implement width can be entered to enablecalculation of the desired paths for the vehicle to follow; to providesuch a system including a display device responsive to the steeringcorrection signal for displaying a needed steering correction for manualsteering control; to provide such a system in which the steeringcorrection signal is applied to an automatic steering mechanism; toprovide such a system which minimizes overshoot in correcting the trackof the vehicle to the desired path; to provide, particularly, a systemwhich repeatedly selects a future intercept point and generates thesteering correction signal to cause the vehicle to move toward theintercept point; to provide such a system which is adapted for guidanceduring parallel swathing and additionally for contour swathing; toprovide such a system which can be conveniently be retrofitted toexisting tractors and vehicles; to provide such a system which can trackand store data defining portions of a field worked, allowing an operatorto resume accurate working of a field following an interruption; and toprovide such a system which is economical to manufacture, which isaccurate and efficient in operation, and which is particularly welladapted for its intended purpose.

[0012] Other objects and advantages of this invention will becomeapparent from the following description taken in relation to theaccompanying drawings wherein are set forth, by way of illustration andexample, certain embodiments of this invention.

[0013] The drawings constitute a part of this specification, includeexemplary embodiments of the present invention, and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram illustrating a swathing guidance systemwhich embodies the present invention.

[0015]FIG. 2 is an elevational view of an exemplary swathing guidancesystem unit by which the present invention is implemented.

[0016]FIG. 3 is a flow diagram illustrating the principal steps of aswathing guidance method which embodies the present invention.

[0017]FIGS. 4, 5, and 6 are geometric diagrams illustrating applicationof the methods of the present invention to returning a vehicle to adesired path.

[0018]FIG. 7 is a simplified geometric diagram illustrating a flaredreturn of a vehicle to a desired path by use of the present invention.

[0019]FIG. 8 is an elevational view of an alternative display unit foruse in the swathing guidance system of the present invention andincorporating linear arrays of indicators for both a steering guidedisplay and a current position display.

DETAILED DESCRIPTION OF THE INVENTION

[0020] As required, detailed embodiments of the present invention aredisclosed herein; however, it is to be understood that the disclosedembodiments are merely exemplary of the invention, which may be embodiedin various forms. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as abasis for the claims and as a representative basis for teaching oneskilled in the art to variously employ the present invention invirtually any appropriately detailed structure.

[0021] Referring to the drawings in more detail, the reference numeral 1generally designates a GPS derived swathing guidance system whichembodies the present invention. The system 1 generally includes aswathing guidance controller or computer 2 and a position detectordevice such as a global positioning system receiver 3. The controller 2stores program routines which receive settings and inputs from switches4 and causes the display of information on the output display devices 5.In particular, the controller 2 cooperates with the GPS receiver 3 tostore detected positions and to determine the extent and direction ofposition or path discrepancy and causes the display of data forcorrective movement on the displays 5.

[0022]FIG. 2 illustrates an exemplary swathing guidance unit 8 whichcomprises most of the components of the system 1, including the inputswitches 4 and the displays 5. In particular, the unit includes a basepanel 10 on which the input switches 4 and the displays 5 are mounted.The illustrated switches 4 include a menu switch 12, an enter or executeswitch 14, a decrement or down switch 16, an increment or up switch 18,a contour mode switch 20, a parallel mode switch 22, and a stop guidanceswitch 24. The displays 5 include a GPS signal quality display 28, asteering guide display 30, a current position display 32, and a menudisplay 34. The guidance controller 2 may be incorporated into theguidance unit 8 or may be a separate module which is plugged into theunit 8. Similarly, the GPS receiver 3 may be built into the guidanceunit 8 or may be implemented as a separate unit which can be mounted onan agricultural vehicle to optimize the position of an antenna orantennas (not shown) of the receiver 3. In such a case, the GPS receiver3 would be connected to the controller 2 by a cable.

[0023] The switches 4 may be formed as membrane switches which have highreliability in agricultural environments which can include high levelsof dust and extremes of temperatures. The GPS indicators 28 and theindicators of the steering guide display 30 and the current positiondisplay 32 may be light emitting diodes (LED's) or fluorescent displays.GPS receivers typically must receive signals from at least four GPSsatellites in order to calculate the current coarse position. Thereceiver 3 must also receive a signal from a differential GPStransmitter in order to calculate the needed fine position possible withdifferential GPS technologies. The differential correction signals cancome from satellite or ground based sources, including C and L bandsatellites, 300 KHz beacon towers, VHF or UHF radio links, and cellphone or internet based communication systems.

[0024] The GPS signal quality display 28 indicates the quality of GPSsignal which is currently being received. The illustrated GPS signalquality display 28 includes a “no-signal” indicator 38, a GPS indicator39, and a DGPS (differential GPS) indicator 40, which may be differentlycolored to indicate function. Alternatively, single, multi-coloredindicator could be employed for the signal quality display 28. Theno-signal indicator 38 is activated when an insufficient number of GPSsatellites are “visible” to the GPS receiver 3. The GPS indicator 39indicates coarse GPS functioning, while the DGPS indicator 40 indicatesfull differential GPS signal acquisition.

[0025] The illustrated steering guide display 30 includes a semicircularor arcuate array of steering guide indicators 42 which, when activated,indicate a steering correction angle to place the guided vehicle on thedesired path. The steering guide display 30 also includes a line ofcurrent heading indicators 43 which are centered on the steering guide30 and form a reference for the steering correction angle to graphicallydisplay a steering or turn correction angle. Although not illustrated,the steering guide display 30 may include angled lines converging at anorigin or center of the display 30 to aid a vehicle operator in readingthe steering guide display 30. The current heading indicators 43 may bea different color than the remaining steering guide indicators 42 forvisual contrast.

[0026] The illustrated current position display 32 is formed by a lineararray of position indicators 46 including a centered, current positionindicator 47. At least one of the position indicators 46 is activated,along with the current position indicator 47, to indicate the relativedistance of a guided vehicle from the desired path and the relativedirection therefrom, that is, to the left or right of the currentposition. The current position indicator 47 is preferably of a differentcolor than the remaining position indicators.

[0027] The display indicators 38-40, 42, 43, 46, and 47 may be lightemitting diodes or fluorescent displays. It is foreseen that thesteering guide 30 and current position display 32 could, alternatively,be implemented as analog meters, graphic displays on a conventionalcathode ray tube (CRT) or liquid crystal display (LCD) monitor, or as aproprietary LCD display showing angularly arrayed regions for thesteering guide display 30 and linearly arrayed functions for the currentposition display 32. The steering guide 30 and current position display32 could, alternatively, be implemented as respective linear arrays ofindicators, as shown in an alternative display unit 33 (FIG. 8) whichwill be described further below.

[0028] The illustrated menu display 34 is preferably a dot matrix LCDdisplay with a capacity for displaying several lines of multiplecharacters. The menu display 34 operates in cooperation with theswitches 4 to enable a vehicle operator to select programmed functionsof the system 1, to enter data, such as implement width, and togenerally control operation of the system 1. An operating program forthe system 1 is stored in memory 50 which is interfaced to thecontroller 2. The memory 50 may include a combination of read onlymemory (ROM), non-volatile read/write memory (RAM), and volatile RAM.The program menu is entered by operation of the menu switch 12. The downand up switches 16 and 18 are used to step or scroll through the menuselections. The enter switch 14 is used to select a function displayedon the menu display 34. The contour and parallel switches 20 and 22 areused to enter respective contour and parallel guidance modes. The stopguidance 24 is used to exit a guidance mode. The menu display 34 mayalso be used in cooperation with the steering guide display 30 andcurrent position display 32 to display numeric values of the heading andposition information graphically displayed by the steering display 30and the position display 32.

[0029] The system 1 is principally described with reference to asteering correction angle which is displayed on the steering guidedisplay 30. However, it is foreseen that a steering correction anglewhich is calculated by the controller 2 could also be applied to anautomatic steering mechanism 52 (FIG. 1), such as a mechanismincorporating hydraulic or electromotive elements to steer a vehicleguided by the system 1. Such an automatic steering mechanism 52,controlled by the system 1 of the present invention, would beadvantageous in agricultural applications as well as non-agriculturalapplications. In an agricultural application, such an automatic steeringmechanism 52 could be used, even with an operator present, to reduceoperator fatigue. Alternatively, some entirely unattended applicationsare envisioned.

[0030]FIG. 3 illustrates principal steps of a swathing guidance method60 according to the present invention. The method 60 includes storingdata defining a desired path for the guided vehicle at 62. The method ofcharacterizing a desired path varies depending on whether a parallelmode or a contour mode has been set by operation of the switches 22 or20. In the parallel mode of operation, GPS position readings are takenat a beginning point and an end point of a reference line or path. Thewidth of the cultivation implement drawn by the guided vehicle isentered by way of the menu and arrow switches 12, 16, and 18. Usingknown geometric and trigonometric relationships, the controller 2 canthen calculate a plurality of paths parallel to the reference line,on-the-fly during operation. Alternatively, the controller 2 cancalculate the paths and store them in the memory 50. Contour modeoperation is somewhat different. In the contour mode, the guided vehicleis driven along a desired contour path with the GPS receiver 3 providingperiodic position readings which are stored in the memory 50. Thecontroller 2 can be programmed to detect when a second pass is begunwhich comes within a selected proximity, such as a multiple of theimplement width previously entered. As each pass is driven, datadescribing the pass is added to the reference data for the next pass.

[0031] Referring to FIG. 3, once a reference path has been stored and acurrent path calculated, an initial GPS reading is taken at 64 and aftera wait or time out 66, enters a steering correction loop 67. Eachsteering correction loop includes an additional GPS reading at 68,followed by a comparison step 70 which compares position data fromcurrent and previous readings by the controller 2, a calculation step 72in which the current speed and heading of the guided vehicle arecalculated, and a store step 73 in which the current speed and headingare stored in the memory 50. The controller 2 selects a future interceptpoint on the stored or projected path at 74, based on the current groundspeed of the guided vehicle. The distance to the intercept point isselected to quickly lead the guided vehicle back onto the desired pathwith minimal overshoot. If the intercept point is at too great adistance, the system 1 will not detect small steering errors. However,if the intercept distance is too small, the steering guide display 30might become erratic and difficult to read. Once the intercept point isselected, the controller 2 calculates a steering correction angle at 76to point the guided vehicle toward the intercept point. Unless operationof the stop guidance switch 24 is detected at 78, the steeringcorrection loop 67 repeats after a timed wait 80. This timed wait is thetime until a new GPS position is received from the GPS receiver 3, whichtypically occurs, in the system 1, every 0.2 seconds. Thus, the GPSreceiver 3 and controller 2 preferably have adequate throughput torepeat the steering correction loop 67 numerous times per second, suchas five times per second.

[0032] The steering correction angle calculated at 76 is used togenerate a “steering correction signal” with a parameter proportional tothe steering correction angle. The steering correction angle is scaledto the angular resolution of the steering guide display 30 so thatsteering indicators 42 and 43 are activated to represent the steeringcorrection angle as accurately as possible. Additionally, the controller2 calculates a distance of the current position from the nearestposition on the desired path as a current position signal and displays arelative distance and relative direction (left or right) to the desiredpath by activation of a generally proportional number of positionindicators 46 and 47. Because of the high update rate of the steeringcorrection loop 67, the controller 2 preferably exercises some “updatesmoothing” techniques to thereby smooth out updates to the indicators ofthe displays 30 and 32 over time to thereby increase usability of thedisplays 30 and 32. If the steering correction signal is applied to anautomatic steering mechanism 52, some update smoothing techniques mayalso be desirable to avoid erratic operation of the steering mechanism52.

[0033] FIGS. 4-6 diagrammatically illustrate use of the system 1 andmethods of the present invention to correct the heading of a guidedvehicle 85, represented by an arrow. Relative distances and angles inFIGS. 4-6 are exaggerated for explanatory purposes. Line PP representsthe desired path and HH the current heading. T is the track error or theperpendicular or closest distance of the vehicle 85 from the path PP. Itshould be noted that although the path PP is shown vertically in FIGS.4-6, possibly appearing to imply a south to north path as onconventional maps, no such restriction in path direction is intended.The controller 2 selects an intercept point IC on the path PP andcalculates a steering correction angle S to point the vehicle 85 towardthe intercept point IC. In FIG. 4, the steering guide display 30 andposition display 32 have respective indicators activated (illustrated asblackened) to display the steering correction angle S and the positionerror T. It should be noted that the steering guide display 30 in thesystem 1 displays the correction angle, not the steering error angle E.The steering error angle E is the angular relationship between thecurrent heading HH and the desired path PP.

[0034] It should be noted that the steering correction quantity may becalculated in units other than S angular units. Referring to FIG. 4,line X-IC is perpendicular to line HH, and line Y-IC is perpendicular toline PP. Lines X-IC and Y-IC are alternative ways of determining a“future crosstrack error”, either by referencing to the current headingHH (X-IC) or to the desired path PP (Y-IC). By trigonometric identities,both lines X-IC and Y-IC are proportional in length to angle S, for agiven distance between the vehicle 85 and IC. Thus, the requiredsteering correction can be calculated in length units instead of angularunits.

[0035]FIG. 5 shows the vehicle 85 reoriented toward the intercept pointIC in response to the displayed steering correction angle, resulting inno steering correction angle shown on the steering guide display 30. Thetrack or position error in FIG. 5 has diminished to T′.

[0036]FIG. 6 shows the vehicle 85 at a somewhat later time as it hasmoved along the new heading from FIG. 5, such that the position errorhas reduced to T″. The controller 2 and the method 60 have selected anew intercept point IC′ on path PP and calculated a new steeringcorrection angle S′. However, the steering correction angle S′ is now tothe left as viewed and as indicated on the steering guide 30. Thecurrent position display 32 indicates that the position error T″ hasbeen reduced from that detected in FIGS. 4 and 5.

[0037]FIG. 7 graphically illustrates, with some spatial exaggeration,the desired corrective effect of the system 1 and method 60. Theselection of the intercept points and calculation of the correspondingsteering correction angles leads the vehicle 85 from an error point Aalong corrective heading path H to a convergence with a generalized pathPP at C, with minimal overshoot.

[0038]FIG. 8 illustrates an alternative embodiment of an display unit 33which includes a steering guide display 30 and a current positiondisplay 32, formed by respective linear arrays of indicators.Specifically, the steering guide display 30 is formed by steeringindicators 90, including a centered current heading indicator 92. In alike manner, the current position display 32 is formed by positionindicators 94, including a centered current position indicator 96. Thesteering guide display 30 may include a centered index indicator 98 tovisually emphasize the center of the display unit 33. The illustrateddisplay unit 33 also includes auxiliary displays 100 which may be sevensegment displays, alphanumeric displays, or dot-matrix arrays. Thedisplays 30, 32, and 100 are interfaced to the guidance controller 2 andreceive activation signals therefrom. The auxiliary displays 100 areused in cooperation with switches 4 to select menu functions of thecontroller 2. The steering guide display 30 and the current positiondisplay 32 of the display unit 33 function in a manner similar to thecorresponding displays 30 and 32 of the unit 8 to graphically displayindications of the quantity and sense of corrective steering actions tomaintain a vehicle 85 on the desired path PP.

[0039] It is to be understood that while certain forms of the presentinvention have been illustrated and described herein, it is not to belimited to the specific forms or arrangement of parts described andshown.

What is claimed and desired to secure by Letters Patent is:
 1. Aguidance method for guiding a vehicle and comprising the steps of: (a)storing data defining a vehicle path in a guidance controller; (b)moving a vehicle in spatial relation to said path; (c) detecting aposition of said vehicle in relation to said path using a positiondetecting system; (d) automatically selecting, by said controller, afuture intercept point on said path; (e) generating a steeringcorrection signal having a steering correction parameter substantiallyproportional to a steering correction angle which would cause saidvehicle to intercept said intercept point; (f) steering said vehicletoward said intercept point in response to said steering correctionsignal; and (g) periodically repeating steps (c), (d), (e), and (f) tothereby place or maintain said vehicle on said vehicle path.
 2. A methodas set forth in claim 1 and including the steps of: (a) interfacing asteering guide display device to said controller; (b) coupling saidsteering correction signal to said steering guide display device tothereby display an angular steering correction substantiallyproportional to said steering correction angle; and (c) manuallysteering said vehicle substantially commensurate with the displayedangular steering correction.
 3. A method as set forth in claim 2 andincluding the steps of: (a) interfacing an arcuate array of visualsteering indicators with said controller; (b) visually designating asubstantially centered reference heading indicator to thereby associatesaid reference heading indicator with a current vehicle heading; and (c)activating at least one of said steering indicators in response to saidsteering correction signal in such a manner as to display said angularsteering correction, relative to said current vehicle heading.
 4. Amethod as set forth in claim 1 and including the steps of: (a)interfacing to said controller a position display device operable todisplay a relative lateral distance and a relative lateral direction ofsaid path from said vehicle; and (b) coupling a path error signal tosaid position display device to cause same to display said relativelateral distance and relative lateral direction of said path from saidvehicle.
 5. A method as set forth in claim 4 and including the steps of:(a) interfacing a linear array of visual position indicators with saidcontroller; (b) visually designating a substantially centered currentposition indicator to thereby associate said current position indicatorwith a current position of said vehicle; and (c) activating at least oneof said position indicators in response to said path error signal tothereby visually display said relative lateral distance and relativelateral direction of said path from said current position.
 6. A methodas set forth in claim 1 wherein said path constitutes a first path andincluding the steps of: (a) entering data representing a path offsetdistance into said controller; (b) calculating, by said controller,offset path data representing an offset path of said vehicle which islaterally offset from said first path by substantially said offset pathdistance; and (c) performing said detecting, automatically selecting,generating, steering, and periodically repeating steps in relation tosaid offset path.
 7. A method as set forth in claim 1 and including thesteps of: (a) interfacing an automatic steering mechanism to saidcontroller; and (b) coupling said steering correction signal to saidsteering mechanism to cause same to steer said vehicle toward saidintercept point.
 8. A method as set forth in claim 1 and including thestep of: (a) detecting said current position using a satellite basedglobal positioning system receiver.
 9. A swath guidance method forguiding an agricultural vehicle in working a field and comprising thesteps of: (a) storing, in a guidance controller, first path datarepresenting path coordinates defining a first agricultural vehiclepath; (b) moving said vehicle in relation to said first path; (c)detecting a position of said vehicle using at least a satellite basedglobal positioning system receiver coupled to said controller; (d)automatically selecting, by said controller, a future intercept point onsaid first path; (e) generating a steering correction signal having asteering correction parameter substantially proportional to a steeringcorrection angle which would cause said vehicle to intercept saidintercept point; (f) steering said vehicle toward said intercept pointin response to said steering correction signal; and (g) periodicallyrepeating steps (c), (d), (e), and (f) to thereby place or maintain saidvehicle on said first path.
 10. A method as set forth in claim 9 andincluding the steps of: (a) interfacing a steering guide display deviceto said controller; (b) coupling said steering correction signal to saidsteering guide display device to thereby display an angular steeringcorrection substantially proportional to said steering correction angle;and (c) manually steering said vehicle substantially commensurate withthe displayed angular steering correction.
 11. A method as set forth inclaim 10 and including the steps of: (a) interfacing an arcuate array ofvisual steering indicators with said controller; (b) visuallydesignating a substantially centered reference heading indicator tothereby associate said reference heading indicator with a currentvehicle heading; and (c) activating at least one of said steeringindicators in response to said steering correction signal in such amanner as to display said angular steering correction, relative to saidcurrent vehicle heading.
 12. A method as set forth in claim 9 andincluding the steps of: (a) interfacing to said controller a positiondisplay device operable to display a relative lateral distance and arelative lateral direction of said first path from said vehicle; and (b)coupling a path error signal to said position display device to causesame to display said relative lateral distance and relative lateraldirection of said first path from said vehicle.
 13. A method as setforth in claim 12 and including the steps of: (a) interfacing a lineararray of visual position indicators with said controller; (b) visuallydesignating a substantially centered current position indicator tothereby associate said current position indicator with a currentposition of said vehicle; and (c) activating at least one of saidposition indicators in response to said path error signal to therebyvisually display said relative lateral distance and relative lateraldirection of said first path from said current position.
 14. A method asset forth in claim 9 and including the steps of: (a) entering into saidcontroller implement width data representing an implement width which isan effective width of said vehicle; (b) calculating, by said controller,offset path data representing an offset path of said vehicle which islaterally offset from said first path by substantially said implementwidth; and (c) performing said detecting, automatically selecting,generating, steering, and periodically repeating steps in relation tosaid offset path.
 15. A method as set forth in claim 9 and including thesteps of: (a) interfacing an automatic steering mechanism to saidcontroller; and (b) coupling said steering correction signal to saidsteering mechanism to cause same to steer said vehicle toward saidintercept point.
 16. A swath guidance apparatus for guiding anagricultural vehicle in working a field and comprising: (a) positiondetector circuitry positioned on said vehicle and operative to detect acurrent geographic position and to output data representing geographiccoordinates of said geographic position; (b) a swath guidance controllerhaving said position detector circuitry coupled thereto and includingdata storage circuitry; (c) a steering guide display visually displayinga representation of a steering correction angle; and (d) said positiondetector circuitry, said controller, and said display cooperating tostore data representing a vehicle path, to periodically compare acurrently detected position with a selected intercept point on saidvehicle path, to calculate said steering correction angle to change aheading of said vehicle toward said intercept point, and to causedisplay on said steering guide display of a representation of saidsteering correction angle.
 17. An apparatus as set forth in claim 16wherein said steering guide display includes: (a) an arcuate array ofvisual steering indicators coupled to said controller; (b) a referenceline including an array origin and intersecting a reference steeringindicator, said reference line being associated with a current vehicleheading; and (c) said controller and said steering indicatorscooperating to activate at least one of said steering indicators tothereby display said representation of said steering correction anglerelative to said reference line.
 18. An apparatus as set forth in claim16 and including: (a) a position display device coupled to saidcontroller and operable to display a relative lateral distance and arelative lateral direction of said path from said vehicle; and (b) saidcontroller generating a path error signal to cause said position displaydevice to display said relative lateral distance and relative lateraldirection of said path from said vehicle.
 19. An apparatus as set forthin claim 18 wherein said position display device includes: (a) a lineararray of visual position indicators coupled to said controller; (b) asubstantially centered one of said indicators being visually designatedas a current position indicator to associate same with a currentposition of said vehicle; and (c) said controller causing at least oneof said position indicators to be activated in such a manner as todisplay said relative lateral distance and relative lateral direction ofsaid path from said vehicle.
 20. An apparatus as set forth in claim 16and including: (a) an automatic steering mechanism mounted on saidvehicle and operable to steer said vehicle; and (b) said steeringmechanism being interfaced to said controller in such a manner as tosteer said vehicle in response to said steering correction anglecalculated by said controller.
 21. An apparatus as set forth in claim 16wherein said position detector circuitry includes: (a) a satellite basedglobal position system receiver.